The present disclosure relates to semiconductor devices, and more particularly to semiconductor devices using nitride semiconductors and including a protecting element.
Nitride semiconductors are compound semiconductors that are formed by compounds of aluminum (Al), boron (B), gallium (Ga), or indium (In) as a group III element and nitrogen (N) as a group V element, and is represented by the general formula BwAlxGayInzN (where w+x+y+z=1, and 0≦w, x, y, z≦1).
Nitride semiconductors have advantages such as a high breakdown voltage, a high electron saturation velocity, high electron mobility, and a high electron density in a hetero junction, due to their wide bandgaps. Nitride semiconductors having different bandgaps are obtained by changing the composition ratio of the group III elements. Hetero junction structures in which layers of nitride semiconductors having different bandgaps are laminated together, or quantum well structures or superlattice structures in which a plurality of such hetero junction structures are laminated together are capable of controlling the degree of modulation of the electron density in elements. Thus, applications of such structures to short wavelength light-emitting elements, high power high frequency elements, and high frequency low noise amplifying elements have been studied and developed.
One type of semiconductor elements using a heterojunction structure is a heterojunction field effect transistor (HFET). HFETs are elements that operate at a high speed, and are expected to be applied to high power elements, power switching elements, high frequency power devices, high frequency low noise amplifiers, and the like.
Reduction in size is desired for semiconductor devices, and HFETs for use in such applications are no exception. However, regarding HFETs using nitride semiconductors, reduction in size of control electrodes (gate electrodes) is limited due to the surge breakdown voltage of the control electrodes. In particular, a further increase in surge resistance is required for power switching elements and the like.
One known method for increasing the surge resistance of an HFET using nitride semiconductors is to connect a protecting diode to a control electrode thereof. Using a pn junction diode, which is formed on the same substrate as the HFET, as such a protecting diode is also considered to reduce the size of semiconductor devices (see, e.g., Japanese Published Patent Application No. 2007-59882).